The use of nasal Continuous Positive Airway Pressure (nasal CPAP) to treat Sleep Disordered Breathing (SDB), for example Obstructive Sleep Apnea (OSA), was invented by Sullivan (See U.S. Pat. No. 4,944,310). Such treatment is typically accomplished using a source of air at positive pressure (e.g., a blower or flow generator) connected to a patient interface (e.g., a mask) via an air delivery conduit. To maintain a suitable pressure at the entrance to the patient's airways, it is necessary to provide a suitable seal between the patient interface and the patient's face. Early masks were glued to a patient's face every night. Today, however, the patient interface is usually held in position with headgear. Treatment is very successful in reducing SDB. However, gas pressurized in the range of 4-20 cmH2O can be noisy and uncomfortable. Poorly fitting masks can provide an inadequate seal against leak. After wearing a mask all night, some patients can have pressure sores on their faces, especially in such sensitive regions as the nasal bridge. Thus, mask designers and manufacturers are constantly striving to provide patient interfaces which provide a comfortable seal.
A variety of masks are available, such as nasal, full-face, and nose and mouth masks.
ResMed's MIRAGE® mask provided a significant improvement in masks for CPAP treatment. FIGS. 1-3 illustrate an embodiment of ResMed's MIRAGE® mask. It is available in both nasal and full-face versions. In the illustrated embodiment, the mask 2 includes (i) a rigid shell or frame 3 that defines a nose-receiving chamber, and (ii) a face-contacting cushion 4. The cushion 4 plays a role in improving the comfort and seal of the mask. For example, see U.S. Pat. Nos. 6,112,746; 6,357,441; 6,581,602 and 6,634,358. Other aspects of the mask, such as a forehead support and vent also play a role in the fit, comfort, and noise of a mask.
As shown in FIGS. 4-6, the cushion 4 of the MIRAGE® mask includes a dual membrane structure. As illustrated, the cushion 4 includes a thinner outer membrane 6 that is spaced away from a thicker inner or underlying membrane 8 at their inner edges.
The present invention is particularly directed towards a cushion with an improved inner or underlying membrane.